my 1997 Pontiac grand prix gtp supercharged series2 3800 missfires (sputters) when accelerating quickly but levels off when at one speed if on highway does same going up hill or passing I have changed plugs and wires still same problem I get codes p0300 p0336 and p0401 please help

All three of those codes can each cause the sputtering problem you are experiencing. The P0300 is a general misfire code meaning you have had or currently have enough misfires on one or more cylinders to set that code. The P0336 code is for the crankshaft position sensor, and the P0401 code is for the exhaust gas recirculation (EGR) system.

Now, a bad crank sensor can cause misfires and also the poor performance you're having, so you might want to start there. Since you've replaced the ignition components, it's probably not that unless you have a bad coil or module.

The EGR issue is for lack of flow, which usually means the system is clogged up with carbon deposits, and is fairly common. This can require EGR valve replacement, or other system components. It would really need to be tested to see what needs to be replaced.